Trailer spring



FIG. 1 is a perspective view at a reduced scale of a trailer spring showing my new design;

FIG. 2 is a left side view thereof, the right side view being a mirror image;

FIG. 3 is a top plan view thereof;

FIG. 4 is a bottom view thereof;

FIG. 5 is a right end view thereof; and,

FIG. 6 is a left end view thereof.

The broken line showing of an axle is for illustrative purposes only and forms no part of the claimed design. 

The ornamental design for a trailer spring, as shown and described. 